1. Field of the Invention
This invention relates to a combustion state-detecting system for detecting a state of combustion (misfiring) in internal combustion engines, based on a variation in the angular velocity of the crankshaft during rotation of the engine in every combustion cycle.
2. Prior Art
Conventionally, a system is known which determines the combustion state of an internal combustion engine, based on a rate of variation in the angular velocity of the crankshaft during rotation of the engine, as proposed, for example, by Japanese Provisional Patent Publication (Kokai) No. 3-286166.
According to the known system, an output from a crank angle sensor is used to detect a rate of variation in the angular velocity of the crankshaft. However, the output of the crank angle sensor always varies due to various factors, such as dimensional errors of the crank angle sensor, dynamic errors of the engine per se, and therefore, the combustion state of the engine cannot be accurately determined.
To overcome this disadvantage, the present assignee has already proposed a method of determining a state of combustion of an internal combustion engine by calculating a rate of variation in the rotational speed of the crankshaft and an average value thereof, and further calculating a cumulative value of the absolute value of the difference between the rate of variation and the average value thereof, followed by comparing the cumulative value with a predetermined value, by Japanese Patent Application No. 4-273632.
However, in the above proposed method, since the rate of variation in the rotational speed of the crankshaft is expressed as a cumulative value of the absolute value of the difference between the rate of variation and the average value thereof, even when the rotational speed turns to an increased side after occurrence of a misfire, the variation in the rotational speed is added to the cumulative value, whereby the cumulative value may exceed the predetermined value. As a result, it is difficult to accurately discriminate the misfiring cylinder.
Further, to discriminate the misfiring cylinder, the use of a complicated algorithm is required, which makes it difficult to promptly discriminate the misfiring cylinder.